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A most thought-provoking article, David, and timely too, as I am consulting at present on piston revisions for a builder of 600 c.i. 8,000 RPM engines whose current rings are perhaps 0.500" down, driven largely by pessimistically deep valve reliefs.
A couple of thoughts:
1. If anti-friction skirt coatings (say Swain's PC-7) were applied thickly to the piston above the top groove, the crevice volume could be reduced to essentially zero without risk of scuffing.
2. Of course if any crevice reduction strategy were to be too effective, the lateral gas ports might be starved for pressure. Perhaps vertical ports would be a better choice, at least initially...
3. Speaking of coatings, I know you were an early proponent of thermal barrier and anti-friction coatings, but I have heard little about them of late. Are they just old news now, or has their lustre faded for some reason? Maybe an update article is called for...
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